The present invention relates to subsurface, or downhole, pumps such as are used to pump oil and other fluids and bases from oil wells, and in particular to valves used in downhole pumps.
When an oil well is first drilled and completed, the fluids (such as crude oil) may be under natural pressure that is sufficient to produce on its own. In other words, the oil rises to the surface without any assistance.
In many oil wells, and particularly those in fields that are established and aging, natural pressure has declined to the point where the oil must be artificially lifted to the surface. Subsurface, or downhole, pumps are located down in the well below the level of the oil. A string of sucker rods extends from the pump up to the surface to a pump jack device, or beam pump unit. A prime mover, such as a gasoline or diesel engine, or an electric motor, or a gas engine on the surface causes the pump jack to rock back and forth, thereby moving the stream of sucker rods up and down inside of the well tubing.
The string of sucker rods operates the subsurface pump. A typical pump has a plunger that is reciprocated inside of a barrel by the sucker rods. The barrel has a standing one-way valve, while the plunger has a traveling one-way valve, or in some pumps the plunger has a standing one-way valve, while the barrel has a traveling one-way valve. Reciprocation charges a chamber between the valves with fluid and then lifts the fluid up the tubing toward the surface.
The one-way valves are designed for hostile environments. The valves are subjected to high pressures (ranging from several hundred psi to several thousand psi), high temperatures and corrosive fluids. The valves include a valve seat and a ball. The valve seat is a ring having a lapped, or shaped, surface for receiving the ball. When the ball engages the seat, the valve is closed. When the ball is disengaged from the seat, the valve is opened. Differential pressure moves the ball into or out of engagement with the seat.
In a typical pump, as the plunger is lifted up, the standing valve in the barrel is opened by the pressure differential across the standing valve; the traveling valve is closed by the pressure differential across the traveling valve. When the plunger is lowered, the standing valve in the barrel is closed, while the traveling valve in the plunger is opened.
Opening a valve is relatively simple; the higher pressure below the valve seat pushes the ball off of the seat, thereby allowing fluid to flow through the valve. Closing a valve involves reversing the pressure differential and guiding the ball back to the seat. An improperly guided ball will have difficulty seating, resulting in improper closure and leaking of the valve.
Valves are provided with ball cages to constrain the movement of the ball and ensure a properly working valve. The cage limits the movement of the ball along a narrow path. The tolerance between the ball and the inside of the cage is small in order to minimize side-to-side movement of the ball. In addition, the cage provides openings around the ball for fluid to flow.
In some prior art cages, the interior of the cage is provided with longitudinally extending ribs, or races. The ribs provide a close tolerance raceway for the ball to move into and away from the seat, while limiting side-to-side movement of the ball. The spaces between the ribs provide the openings for fluid flow.
Some wells produce relatively large quantities of sand. As the sand flows through the valve, it tends to accumulate in the openings around the ball and between the ribs. The sand accumulation chokes off fluid flow and prevents the ball from moving to open and close the valve. A pump with a sand-clogging problem loses efficiency in pumping fluid to the surface.
It is an object of the present invention to provide a valve ball cage for a downhole pump that minimizes sand accumulation in the valve.
The present invention provides a cage for use in a valve of a downhole pump. The cage has a tubular wall having a passage extending between two ends. The passage comprises a ball chamber. The ball chamber is bounded by the wall, a perforated member and a throat that opposes the perforated member. The throat comprises a stop for receiving a seat. A raceway in the ball chamber extends from the throat toward the perforated member and is structured and arranged to receive a ball. The raceway has passages therein. The raceway skews away from a longitudinal axis of the ball chamber from the throat toward the perforated member.
In accordance with one aspect of the present invention, the raceway comprises ribs. In accordance with another aspect of the present invention, the ribs are made of a material that is different than the tubular wall.
In accordance with still another aspect of the present invention, the ribs are made of a material that is harder than the tubular wall. Alternatively, the ribs are made of an elastomeric material.
In accordance with another aspect of the present invention, the ribs are made of a material that is substantially the same as the tubular wall.
The present invention also provides a cage for use in a valve of a downhole pump, which cage comprises a tubular wall having a passage extending between two ends. The passage comprises a ball chamber, with the ball chamber being bounded by the wall, a perforated member and a throat that opposes the perforated member. The throat comprises a stop for receiving a seat. The throat has a first inside diameter. At least portions of the tubular wall on the ball chamber are hardened. The tubular wall of the ball chamber has a second inside diameter between the hardened portions that is larger than the first inside diameter.
The present invention also provides a valve for use in a downhole pump. The valve comprises a cage having a passage extending between two ends, the passage comprising a ball chamber, the ball chamber being between a perforated member and a stop. The ball chamber has a wall extending from the stop to the perforated member. A seat is located in the passage and abuts the stop. A ball is located in the ball chamber between the perforated member and the seat. The ball is movable between a closed position, wherein the ball engages the seat, and an open position, wherein the ball is disengaged from the seat. A raceway is located in the ball chamber and receives the ball. The raceway comprises ribs with channels therebetween. The raceway skews away from a longitudinal axis of the ball chamber from the seat toward the perforated member so that when the ball is in the open position, the ball is offset from the longitudinal axis.
In accordance with one aspect of the present invention, the raceway comprises ribs. In accordance with another aspect of the present invention, the ribs are made of a material that is different than the tubular wall.
In accordance with still another aspect of the present invention, the ribs are made of a material that is harder than the tubular wall. Alternatively, the ribs are made of an elastomeric material.
In accordance with another aspect of the present invention, the ribs are made of a material that is substantially the same as the tubular wall.
The present invention also provides a valve for use in a downhole pump, comprising a cage having a tubular wall with a passage extending between two ends. The passage comprises a ball chamber, with the ball chamber being bounded by the wall, a perforated member and a throat that opposes the perforated member. The throat comprises a stop for receiving a seat in the passage. The throat has a first inside diameter. At least portions of the wall in the ball chamber are hardened. A ball is located in the ball chamber between the perforated member and the seat, with the ball being movable between a closed position, wherein the ball engages the seat, and an opened position, wherein the ball is disengaged from the seat. The valve has a first clearance between the ball and the throat when the ball is located in the throat and has a second clearance between the ball and the hardened portions when the ball is located in the ball chamber. The second clearance is at least twice as large as the first clearance.
The present invention also provides a downhole pump comprising a barrel and a plunger that reciprocates inside the pump. The pump has at least one valve in either the barrel or the plunger. The valve comprises a cage having a passage extending between two ends, the passage comprising a ball chamber, the ball chamber being between a perforated member and a stop. The ball chamber has a wall extending from the stop to the perforated member. A seat is located in the passage and abuts the stop. A ball is located in the ball chamber between the perforated member and the seat. The ball is movable between a closed position, wherein the ball engages the seat, and an opened position, wherein the ball is disengaged from the seat. A raceway is located in the ball chamber and receives the ball. The raceway comprises ribs with channels therebetween. The raceway skews away from a longitudinal axis of the ball chamber from the seat toward the perforated member so that when the ball is in the open position, the ball is offset from the longitudinal axis.
The present invention also provides a downhole pump comprising a barrel and a plunger that reciprocates inside the pump. The pump has at least one valve in either the barrel or the plunger. The valve comprises a cage having a passage extending between two ends, the passage comprising a ball chamber, the ball chamber being between a perforated member and a stop. The ball chamber has a wall extending from the stop to the perforated member. A seat is located in the passage and abuts the stop. A ball is located in the ball chamber between the perforated member and the seat. At least portions of the tubular wall on the ball chamber are hardened. The valve has a first clearance between the ball and the throat when the ball is located in the throat and has a second clearance between the ball and the hardened portions when the ball is located in the ball chamber. The second clearance is at least twice as large as the first clearance.